I can't find any documentation -- I don't think Adobe intended for users to create additional export video presets for the Slideshow module. (Video export presets for the File > Export command are different beasts.)
If you want to experiment, go to the folder /Applications/Adobe Lightroom/Adobe Lightroom/Contents/Plugins/Slideshow.lrmodule/Contents/Resources/presets, and you'll see the Slideshow export presets. They're just text files. You can copy one and edit it, and it will show up in the Export Slideshow To Video window. But I have no idea how well that works.
Thanks for replying John.
I will have to go fetch my mac as on windows slideshow.lrmodule seems to be a dll. I searched the whole application folder for .lrtemplate and found nothing. I did find some old presets from lrtimelapse and tried modifying those and putting them in C:\Users\bryn\AppData\Roaming\Adobe\Lightroom\Video Presets
which comes empty (and to me implies they sort of intended users to be able to create them -- as clearly lrtimelapse developer did)
Well I was able to extract the file from the mac package and modify it but it doesn't appear in the export video -> video presets drop down, when I place it in the windows preset folder. I'm guessing they dropped support for presets. LRTimelapse seems to have gone the video export path.
I was hoping to be able to simply add 4k export support for the slideshow module.
I can't seem to get this website to display the code pasted in but here's a try (I changed all mentions of 1080 to 2160 and changed the resolution):
internalName = â€œ2160P",
I did some poking around, and it appears that on Windows, the slideshow preset templates are hardwired into the "slideshow_module.dll". These templates have the same syntax as on Mac, but because they are embedded in slideshow_module.dll", there is no easy way to add new ones, as on Mac. This difference between the two platforms seems gratuitous, but perhaps there was a good reason for it.